|A cauldron made in 15th century England. Source|
A cauldron is a large kettle used for cooking over a fire. The word itself has its earliest origins in Latin word calēre, which means "to be warm". The first known use of the word was in the 14th century.
Since cauldrons were once a common household object, many folk tales have arose of cauldrons containing magical substances. Old Irish folk legends tell of leprechauns that kept their gold in cauldrons. Since cauldrons used to be used in everyday life for cooking, potions in folklore were often cooked or prepared in cauldrons. A popular example is the three witches in Shakespeare's play Macbeth, in which the three witches brew "a charm of powerful trouble" with several unorthodox ingredients.
In the Harry Potter series, cauldrons are used primarily to brew potions and are usually like normal cooking cauldrons, although there are also accordion-like collapsible cauldrons and self-stirring cauldrons. First year students at Hogwarts are required to buy a pewter cauldron (most utensils and cookware was made of pewter in the middle ages) although they come in a variety of other materials as well.
In Pottermore, cauldrons can be purchased at Potage's Cauldron Shop in Diagon Alley. They come in three types, Pewter Size 2 (15 Galleons) Brass Size 2 (21 Galleons) and Copper Size 2 (25 Galleons). pewter cauldrons brew potions the slowest, brass ones a bit faster, and copper ones the fastest. This is a reference to the use of copper and its alloys in ancient times as a medicine and as a liquid purifier. These practices arose because in real life, copper and many of its alloys (such as bronze) really do kill bacteria.